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1. Upload the entire contact-form-7 folder to the /wp-content/plugins/ directory.
2. Activate the plugin through the 'Plugins' menu in WordPress.

The control panel of Contact Form 7 is in 'Manage > Contact Form 7' (on WordPress 2.7 and greater, 'Tools > Contact Form 7'). Please note that it has moved from the 'Settings' menu since Contact Form 7 1.8.

For basic usage, you can also have a look at the plugin homepage and FAQ.